Thalassa is the second moon of Neptune. Thalassa was named after a daughter of Aether and Hemera from Greek mythology. "Thalassa" is also the Greek word for "sea". It was discovered in 1989 by Voyager 2. It is irregularly shaped and shows no sign of any geological modification.
- Orbital radius: 50,000 km
- Diameter: 80 km
- Mass: Unknown
- Orbital period: 7 hours, 30 minutes (0.311485 days)
- Orbital inclination: 0.21°